The general research goal is the elucidation of the structure, mechanism of catalysis, and role of the phosphorly transferring enzymes in the energy metabolism of the cell. GTP-AMP phosphotransferase from beef heart mitochondria has been purified and crystallized. If suitable crystals can be obtained, X-ray studies in another laboratory will be undertaken, and in our laboratory the amino acid sequence will be determined. Since GTP-AMP phosphotransferase has only two tryptophans, one of which seems essential for activity, fluorescence studies will be conducted. Other phosphoryl transferring enzymes such as adenylate kinase from bakers' yeast are being isolated in quantity in order to study the properties of the molecule. Study of several of these phosphoryl transferring enzymes will lead to a better understanding of the mechanism by which the catalysis is effected.